Unitary field structure for magnetic loudspeaker



1967 z A. L. COEN 3,319,201

UNITARY FIELD STRUCTURE FOR MAGNETIC LOUDSREAKER Original Filed March30, 1961 INVENTOR ALDO L. COEN United States Patent 3,319,201 UNIIARYFIELD STRUCTURE FOR MAGNETIC LQUDSPEAKER Aldo L. Coon, 1640 E. StithSt., Chicago, Ill. 60615 Original application Mar. 30, 1961, Ser. No.99,414, new

Patent No. 3,191,421, dated June 29, 1965. Divided and this applicationJune It), 1965, Ser. No. 474,197

2 tjlaims. (Cl. 335-231) ABSTRACT OF THE DISCLOSURE A speaker pot forthe magnetic circuit of a loudspeaker that is of one-piece homogeneousconstruction and is provided with a unitary inwardly extending annularflange, the inner periphery of which cooperates with a permanent magnetplaced within the speaker pot to form the air gap in the said magneticcircuit.

This application is a division of application Ser. No. 99,4l4, filedMar. 30, 1961, now Patent No. 3,191,421. The invention relates generallyto loudspeakers, and more particularly is concerned with a unitaryspeaker pot for use in the field structure of the magnet circuitutilized with said loud speaker.

The so-called magnetic speaker of today is formed basically of a papercone or diaphragm to which there is secured a voice coil. The output ofa source of audio frequency energy is connected to cause the passage ofalternating current through the voice coil, the amplitude of whichvaries with the intelligence carried by the said output. A magneticfield of very high flux density is established, and the voice coil isarranged so that the turns of Wire are transverse of the principal linesof force of the magnetic field. In accordance with well knownprinciples, the flow of current through the voice coil will tend to movethe individual wires and hence, will move the entire voice coil,vibrating the same in accordance with the audio frequency. Since thecone or diaphragm is secured to the voice coil, the cone is alsovibrated, thereby driving a column of air forwardly and rearwardly ofthe voice coil. This produces the sound waves which are heard from theusual speaker.

This invention is concerned primarily with the field structure of themagnetic circuit which establishes the high magnetic field within whichthe voice coil is adapted to oscillate. Such field structures in thepast have been made of substantially U-shaped members. A typicalstructure consisted of a strip of low carbon steel bent in the form of aU and having a bridging bar or front plate secured across the free endsof the U. The speaker basket is secured to the bridging bar. In thecenter of the bridging bar there was a circular opening within which wasdisposed a steel disc. The diameter of the disc is slightly less thanthe inner diameter of the opening, and the disc was mounted to apowerful permanent magnet of lesser diameter than the disc, thepermanent magnet eX- tending from the disc down to the inner surface ofthe bottom of the U to which it is usually cemented. The flux path, aswill be understood, extends generally along the axial length of thepermanent magnet which is somewhat like the core of a transformer,dividing through the pole piece, passing thence across the gapestablished between the pole piece and the bridging bar, through thearms of the U-shaped field structure and back to the bottom of themagnet. A short section of a cylindrical paper tube is mounted forreciprocal movement in the gap and carries the voice coil usually as alayer or two of fine wire wrapped thereon and held in place 'by shellacor cement. To the upper end of this cylindrical section, often calledthe former, is secured a varnished buckram spider or diaphragm and theinner portion of the speaker cone. The spider in turn is cemented to thebasket of the speaker which, of course, is in the form of a metal frame,and the outer ends of the speaker cone are suspended at the outer endsof the basket. The spider provides the resilient suspension for the apexof the cone.

This structure has been used for many years, especially in low costspeakers of relatively small size. There have been many disadvantages ofsuch speakers. In the first place, the U-shaped field member uses theflux available from the magnet in a very inefficient manner. Since thesides of the U opposite its two legs are open, very substantial fringingof flux from the magnet was created. This caused interference in theapparatus with which the speaker was associated. Another disadvantagewas that only a faction of the voice coil was located in flux fields ofstrong and uniform density, thereby adversely affecting fidelity as wellas rendering the vibration driving of the cone inefficient.

Another important disadvantage of the previous speaker pots, as thefield structures were called, was that they were expensive tomanufacture and there was difficulty in maintaining the properdimensional relationships as required for efficient and properoperation.

Most of the above described disadvantages have been eliminated by theappearance recently of a field structure which completely encloses thepermanent field magnet. This field structure consists of a cylindricaljar-like container in which the permanent magnet is co-axially mounted,and the pole piece substantially closes the top opening of the containerbut for the gap formed between itself and the upper rim of thecontainer. The difiiculty in making such a field structure was thatbecause the upper rim of the container or pot was required to have aflange of substantially lesser inside diameter than the body of thecontainer, an undercut was necessary. This meant that the fieldstructure container had to be manufactured on a screw machine. Besidesbeing wasteful of material in a structure of this kind, the screwmachine operation is very expensive as well, but the advantages to beachieved over previous structures of this kind nevertheless made themachined device popular and successful.

The primary object of this invention is to provide a loudspeaker fieldstructure of a configuration whereby the structure may be made fromsheet steel as a stamping or drawing with accompanying saving ofmaterial, labor and expense.

Many other objects and advantages of the invention will become apparentas a description of the novel article proceeds hereinafter, inconnection with which a preferred embodiment of the invention isillustrated in the accompanying drawings.

In the said drawings:

FIG. 1 is a sectional view taken through a portion of a loudspeaker inwhich the magnetic circuit of the said speaker includes a fieldstructure constructed in accordance with the invention.

FIG. 2 is a perspective view of the completed pot.

The structure of the invention is characterized by the fact that thesame is formed of an integral sheet of steel as a stamping or drawing.

Looking first at FIGS. 1 and 2, the reference character 10 is used todesignate generally the completed field structure itself, and as will beseen, the same comprises a gen erally cylindrical body portion 12 and anintegral circular bottom wall 14 having an interior flat bottom surface16. At its upper end, the pot 10 (as it will often be calledhereinafter) is provided with a radially inwardly extending flange 18having an annular exterior shoulder 20, an annular interior cylindricalsurface 22, and an axially facing end surface 24 of circularconfiguration. Because of the flange 18, it will be appreciated thatthere is a substantial portion of the said flange which overhangs theinterior cylindrical chamber 26 provided in the said pot The criticaldimensions and relationships of the structure described are,substantially accurate parallelism between the inner bottom surface 16of the pot and the upper surface 24 and accurate co-axial relationshipbetween the cylindrical interior of the flange 18 at 22 and the shoulder20.

Before proceeding with a description of the advantageous manner in whichthe pot may be manufactured, attention is invited to FIG. 1 which showshow the pot is used in the construction of a loudspeaker.

The reference character 30 is the so-called speaker basket which isformed of sheet metal in the form of a framework or cage to protect thepaper cone 32 and support the outer periphery thereof. The basket 30 isprovided with a co-axial opening 34 that is of such dimension as toengage upon shoulder 20. The basket 30 is secured in place upon the pct12 in any suitable manner, and it is desirable that the pot and basketbe rigidly connected. A cylindrical permanent magnet 36 is co-axiallycemented to the surface 16, and it has a disc-like pole piece 38 mountedto the top thereof. The diameter of the pole piece 38 is somewhat lessthan the inner diameter of the cylindrical surface 22, thereby toprovide a narrow gap or annular space between the pole piece 38 and theflange 18. This gap or annular space 40 is very narrow, the narrower thebetter, and it will be obvious that from the axis of the pole piece 38and radiating outwardly therefrom, there will be established a high fluxdensity path for the magnetic flux created by the permanent magnet 36.In FIG. 1, the size of the gap is exaggerated for purposes of clarity.

A varnished resilient buckram or linen suspension spider 42 of annularconfiguration and provided with molded concentric grooves is cemented tothe interior of the basket at 44. The inner end or apex of the cone 32is cemented to the diaphragm 42 at 46, and a short cylindrical tube 48of relatively thin paper or cardboard is secured to the cone 32 at 50and extends through the gap 40 co-axially of the pole piece 38. Thisshort tubular section 48 serves as the former for several turns of wire52 which comprise the voice coil, the wire being arranged on the former48 so that the field created by the wire as current passes therethroughwill cut the lines of force extending across the gap 40 between the polepiece and the flange 18. The wires from the coil are shown at 54extending up through the interior of the cone and out through the wallsthereof to the source of audio frequency current. 56 is a felt discwhich protects the mechanism just described from dust. Obviously thesuspension spider 42 serves as resilient means to oppose movement of theformer 48 and the cone 32.

The reasons for maintaining certain of the dimensions 7 of the pot 10will now be obvious. It will also be obvious that the entire cylindricalwall portion 12 comprises a low reluctance path for magnetic flux fromthe permanent magnet 36 and that the chamber 26 is required in order 7There are several important things which should be kept in mind withrespect :to the field structure described. This structure is formed fromsheet material hence the scrap is a minimum. There are no machiningoperations other than that described in connection with the drilling ofthe opening in the pot to form the inner surfaces 22. No annealing isneeded throughout the entire process, since none of the steps thereofare of such radical nature as to require this.

Obviously, throughout this description the words upper and bottom havebeen used to designate the opened and closed ends respectively of thepot 10 regardless of how the pot itself is arranged.

It will be appreciated that variations in thestructure may be madewithout departing from :the spirit or scope of the invention as definedin the appended claims.

What it is desired to secure by Letters Patent in the United States is:

1. An integral, one-piece speaker pot for use with the field structurein the magnetic circuit of a loudspeaker, said speaker pot comprising aone-piece homogeneous cup-like structure of substantially uniform wallthickness having a closed bottom and a cylindrical side wall, aninwardly extending annular flange-like formation on the upper end ofsaid cup-like structure which is a unitary part thereof, said inwardlyextending portion having an opening therein which defines a cylindricalsurface, the diameter of which is substantially less than inner diameterof the cylindrical side wall, said cylindrical surface being adapted,upon the mounting of a magnet in said cup-1ike structure, to cooperatetherewith to define an annular air gap for the said magnetic circuit,and a seat in the interior of said cup-like structure for supporting,said magnet.

2. A structure as claimed in claim 1 in which a loudspeaker basketseating shoulder is provided on the exterior of said flange co-axialwith said cup member.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A.GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner.

1. AN INTEGRAL, ONE-PIECE SPEAKER POT FOR USE WITH THE FIELD STRUCTUREIN THE MAGNETIC CIRCUIT OF A LOUDSPEAKER, SAID SPEAKER POT COMPRISING AONE-PIECE HOMOGENOUS CUP-LIKE STRUCTURE OF SUBSTANTIALLY UNIFORM WALLTHICKNESS HAVING A CLOSED BOTTOM AND A CYLINDRICAL SIDE WALL, ANINWARDLY EXTENDING ANNULAR FLANGE-LIKE FORMATION ON THE UPPER END OFSAID CUP-LIKE STRUCTURE WHICH IS A UNITARY PART THEREOF, SAID INWARDLYEXTENDING PORTION HAVING AN OPENING THEREIN WHICH DEFINES A CYLINDRICALSURFACE, THE DIAMETER OF WHICH IS SUBSTANTIALLY LESS THAN INNER DIAMETEROF THE CYLINDRICAL SIDE WALL, SAID CYLINDRICAL SURFACE BEING ADAPTED,UPON THE MOUNTING OF A MAGNET IN SAID CUP-LIKE STRUCTURE, TO COOPERATETHEREWITH TO DEFINE AN ANNULAR AIR GAP FOR THE SAID MAGNETIC CIRCUIT,AND A SEAT IN THE INTERIOR OF SAID CUP-LIKE STRUCTURE FOR SUPPORTINGSAID MAGNET.